lt1 sucking oil on high vacuum?

[924cgt]

I have an lt1 that runs great and accelerates hard with no oil consumption at all. My problem is that when I engine brake oil is being sucked into my intake somehow, so when I am done engine braking and I touch the gas pedal there is a huge belch of oil smoke. The engine ported heads and ported intake and TB and a hot cam. I have tried everything I know to no avail.

Pinched off the PCV hose- still sucks oil

Replaced intake gaskets (twice) - still sucks oil

Taken apart air oil seperator in intake manifold everything looks fine (pinching off pcv hose bypassed that anyway)

Two new sets of valve stem seals, first tried teflon, then switched to viton- still sucks oil.

used thread sealer on rocker studs - still sucks oil

Even though leakdown and compression numbers showed fine, I even pulled my pistons and threw a new set of rings on. Bores measured within spec, pistons looked nearly new. I honed my bores, went through some hard ring seating cycles, and low and behold... she still sucks exactally the same amount of oil on trailing throttle.

WTF? Any input would be appreciated!

[cocobolo95]

Do you have the fresh air intake hose attached to valve cover? And the hose that goes to pvc valve? Have you tested the pvc valve itself for proper function. If you pm me with your e-mail address I'll send you the pages from factory service manual on pvc system with test of pvc valve.

[924cgt]

Originally Posted by cocobolo95

Do you have the fresh air intake hose attached to valve cover? And the hose that goes to pvc valve? Have you tested the pvc valve itself for proper function. If you pm me with your e-mail address I'll send you the pages from factory service manual on pvc system with test of pvc valve.

The fresh air intake is connected between the TB and the valve cover. I have tested the pcv valve and it is ok. I also assumed that blocking the pcv hose entirely would eliminate that as a possibility... no?

[95 Firehawk]

Are you sure it's oil? You said you have no oil consumption, from what you describe you should show some evidence of oil loss. How do the plugs look? Is there a lot of oil deposits in the intake?

I used to have a lot of oil pulled through the breather on the passenger side valve cover through the TB that dirtied up my intake valve pretty bad. I found a breather filter from AutoZone that fit perfectly and kept my intake much cleaner. Didn't have the same issue as you though.

[bobdec]

Do you have excessive blow-by ? At idle, pull fresh air hose hose from pass valve cover to TB, hold a sheet of paper over the hole, PVC suction (slight vac in crankcase) should hold the paper snug against the hole. That says PVC valve is open & working. Works that way at normal/high intake vac conditions. At No/low intake vac conditions (acceleration) the flow reverses PVC valve closes, TB high air flow ventura effect then starts sucking air through that hose to TB to keep a slight vac in crankcase. That's when oil can enter the intake, it dirties up intake & TB blades, high modded engines use breathers/collectors to prevent oil to intake, but it should not be enough to show blue smoke later on.

The only other ways for oil to get to cylinders is from Intake galley (intake manifold gasket), valve train (valve seals) or crankcase (rings). And you have done all that !! Maybe time to ask over in 'Advanced Tech' Advanced Tech - CamaroZ28.Com Message Board

[924cgt]

I placed a piece of paper over the hole in the passenger valve cover and it stuck from the crankcase vacuum at warm and cold idle. The vacuum seemed very weak, but you could tell it was there. How many psi of vacuum is the crankcase supposed to have at idle?

[95 Firehawk]

There is no spec on how much vacuum should be pulled, only that it is present indicating the fumes are being pulled into intake air. Was there evidence of excessive oil in that hose? The more tired the engine, the more blow-by occurs when under load, and the more oil will be sent back through that hose to the TB.


Sent from my iPhone using Autoguide.com App

[924cgt]

I have driven the car with the fresh air hose removed and the pcv valve hose pinched off and there is still the same oil sucked on high vacuum. So what does that mean? I am begenning to wonder if the angle of my heads does not match my intake manifild.?

[95 Firehawk]

The oil wouldn't pass through the pcv valve under load, only under closed/part throttle will the engine be pulling vacuum through there. Under heavy load, the flow tries to reverse when pressure from blow by and the venturi effect at the TB, causing th pcv valve to close. Pinching it off wouldn't help anything. The breather hose on the passenger side is where oil will travel through into the TB; it has nothing to do with the pcv valve.

[924cgt]

Originally Posted by 95 Firehawk

The oil wouldn't pass through the pcv valve under load, only under closed/part throttle will the engine be pulling vacuum through there. Under heavy load, the flow tries to reverse when pressure from blow by and the venturi effect at the TB, causing th pcv valve to close. Pinching it off wouldn't help anything. The breather hose on the passenger side is where oil will travel through into the TB; it has nothing to do with the pcv valve.

The engine is not suckuing oil under a load. Under a load there is no oil smoke at all. Long runs of hard engine braking cause it to suck oil. (evident when you hit the gas again from one puff of smoke, only seen after a long trailing throttle.) High vacuum, it sucks oil... even with the PCV hose pinched shut. The leakdown numbers are good, the rings are new, the valve stem seals are new, and the intake gaskets are new. I am now wondering if maybe it might somehow be the intake gaskets still. Is there a crap vs good on intake gaskets?

[95 Firehawk]

I imagine that's really the only thing left where oil could be pulled from. Since the leak down test was good, that would seem to rule out rings, valve seals, and head gaskets. Since the crankcase ventilation is a closed system, you could try plugging the pcv, then checking for vacuum at the fresh air hose (passenger side valve cover) again. If there's still vacuum present (you may want to check this during deceleration too), that would seem to point to an intake gasket leak, pulling air (and oil) in from the lifter valley.